Dengue (DEN) viruses continue to cause major epidemics throughout the tropical and subtropical regions of the world. At the present time there are no dengue virus vaccines available. The DEN virion envelope (E) protein stimulates protective virus neutralizing antibodies and is an ideal vaccine candidate. Work has been undertaken to biosynthetically produce authentic DEN virus E protein in two expression systems. Sindbis (SIN) virus replicons and recombinant vaccina viruses. Modification of the DEN virus cloned gene insert to include the carboxyl terminal region of the DEN virus capsid protein facilitated expression and secretion of prM/E protein by both systems. Enhanced levels of prM/E protein were secreted into the medium when at least 15 amino acids of the carboxyl portion of the capsid protein and basic amino acids of the cleavage site were included. Secreted prM/E particles could be separated from soluble proteins by dentrifugation and probably represent the slowly sedementing hemagglutinin (SHA). Studies are currently underway to enhance production of these antigens and initiate monclonal antibody analysis of their antigenic structure, ability to stimulate neutralizing antibodies and provide protection from DEN virus infection.